Exogenous riboflavin activates stress-responsive gene networks in Arabidopsis

Riboflavin is the precursor of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), vital coenzymes for a wide array of plant metabolic processes, supporting photosynthesis, mitochondrial electron transport and fatty acid oxidation. While exogenous riboflavin application has been reported to improve plant responses to a range of abiotic and biotic stresses, the molecular responses associated with these protective effects remain largely unknown. Here, we present a comprehensive transcriptomic analysis of riboflavin-treated Arabidopsis seedlings, revealing significant changes in gene expression related to stress responses, signal transduction and secondary metabolism. Riboflavin treatment altered the expression of genes within specific cellular functional categories, suggesting a broad reprogramming of plant metabolism. Exogenous riboflavin caused pronounced changes in the expression of stress-responsive transcriptional regulators, including DREB19 and DREB2C, which are involved in stress-responsive signalling pathways. The transcriptional changes were consistent with a shift from growth-associated to stress-responsive functions, including repression of photosynthesis-related genes and activation of pathways associated with oxidative stress responses. These transcriptomic findings were accompanied by changes in cellular redox status, as riboflavin-treated seedlings exhibited reduced ROS accumulation, lower malondialdehyde levels, indicative of diminished lipid peroxidation and temporally regulated activities of CAT, SOD and APX. Furthermore, exogenous riboflavin altered the expression of genes involved in flavin metabolism, including FMN/FHY, which encodes a key bifunctional enzyme catalyzing the interconversion of riboflavin and FMN in the cytosol. Collectively, these results indicate that an acute increase in riboflavin availability triggers coordinated transcriptional and redox responses associated with stress-related pathways and flavin metabolism, highlighting the importance of tightly regulated riboflavin homeostasis in plants.